size of the left side is 2-by-1 and the size of the right side is 1-by-1001

Question

Abdullah 2022-11-19

0
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https://ww2.mathworks.cn/matlabcentral/answers/1856953-size-of-the-left-side-is-2-by-1-and-the-size-of-the-right-side-is-1-by-1001

回答： DGM 2022-11-19

I am encountering an error message saying that "Unable to perform assignment because the size of the left side is 2-by-1 and the size of the right side is 1-by-1001."

But I do not know what is the problem.

Would you please help me figure out the problem?

The function is as following:

function u = f_semi_imp_euler(u0, tend, nsteps, k, m)
dt = tend/double(nsteps);
u = zeros(2, nsteps+1);
u(:,1) = u0;
Ma = [1-(dt^(2))*(k/m) dt; -dt*(k/m) 1];
for i = 1:nsteps
    u(:,i+1) = Ma*u(:,i);
end
end

-----------------

The code that I am getting an error message from:

T = 10.0; % Final time until which we compute
N = [1000, 750, 500, 250, 100, 75, 50, 10]; % Number of time steps
k = 5;
m = 0.5;
% Initial values
x0 = 1.0;
v0 = 0.1;
u0 = [x0;v0];
alpha = sqrt(k/m); % Computing alpha for linear solution
% Computing parameters A and B for exact linear solution 
A = v0/alpha;
B = x0;
% Computing exact linear solution
u_exact = @(t) [A*sin(alpha*t)+B*cos(alpha*t); v0*cos(alpha*t)-x0*alpha*sin(alpha*t)];
err_semi_imp = zeros(2,length(N));
dts = zeros(1,length(N));
for n = 1:length(N)
    taxis = linspace(0, T, N(n)+1);
    u_semi_imp_euler = f_semi_imp_euler(u0, T, N(n), k, m);
    
    dts(n) = taxis(2) - taxis(1);  % store the time step dt for plotting
    % Now compute the errors
    err_semi_imp(:,n) = max(abs(u_semi_imp_euler - u_exact(taxis)));
end